The invention relates to a rectangular foldable sheet of the type used for maps and advertising brochures, for example.
According to German Patent reference DE-GM No. 68 07 085, a foldable sheet of this type is provided in such a manner for a map printed on two sides with different scales that when the foldable sheet is completely opened, the entire map on the one scale is visible, whereas when the foldable portions are folded back onto the central portion which remains unfolded, the other map scale is visible. In the folded state, this map still shows a quarter of the surface area of its opened state. By partial folding, it is possible to form also a combination of the representation of the front with the representation of the back, such as, for example, in advertising brochures in which it is thus possible to combine a text with an image. The possible combinations using this foldable sheet are, however, limited.
Generally, foldable sheets are known in which at each unfolding along a folded edge the surface area is increased to twice the value. This results in unfoldings of large surface area which is not very practical especially in limited spaces, for example in a vehicle. In addition, when unfolding, in each case only one side of the sheet can be rendered visible. In the case of sheets printed on both sides, the unfolded sheet must be turned over completely in order to render the rear side visible.
In addition, there is the concertina type folding format in which a zig-zag-like folding of an elongate sheet of paper permits a space-saving folding up. In this case, however, it is disadvantageous that a pictorial representation must always extend in a preferred direction, to which principle cartographic accuracy must frequently give way, for example in the case of concertinas of the course of a river.